JP4017631B2 - System and method for detecting rotational stall in a centrifugal compressor - Google Patents

Description

[Cross-reference of related applications]
This application is filed with US provisional patent application no. It claims the benefits of 60 / 405,374.

  The present invention generally relates to detection of rotational stall in a centrifugal compressor. More particularly, the present invention relates to a system and method for detecting rotational stall in a diffuser portion of a centrifugal compressor by sensing acoustic energy changes in discharge from the centrifugal compressor.

  Rotational stall in a centrifugal compressor may occur in the rotating impeller or rotor of the centrifugal compressor or in a stationary diffuser downstream from the impeller and downstream of the centrifugal compressor. The frequency of energy associated with swivel stalls typically ranges from a common range of values whether swirl stalls occur in the impeller region (impeller swirl stalls) or in the diffuser region (diffuser swivel stalls). Is inside. In both cases, the presence of swirling stall can adversely affect the performance of the centrifugal compressor and / or system. However, impeller turning stall is usually of greater concern. This is because impeller swivel stalls can adversely affect impeller reliability, particularly in axial compressors such as aircraft engines, whereas diffuser swivel stalls typically affect the overall sound and vibration level of the system. is there.

  Some techniques for detecting and correcting impeller turning stalls use a plurality of sensors arranged circumferentially adjacent to the rotating impeller. Sensors are used to detect disturbances at individual positions. The disturbance is then compared to values at other locations or values corresponding to optimal operating conditions. Often, very complex calculations are performed to determine the precursors of impeller turning stalls. Once an impeller swirl stall is detected, some corrective action can be taken to bleed the discharge gas back to the suction inlet of the centrifugal compressor, or by using a baffle or changing the vane position and the angle of the inlet inlet flow. Including changing.

  An example of a technique for detecting impeller rotation stall in an axial compressor is disclosed in US Pat. 6,010,303 (hereinafter referred to as "303 patent"). The 303 patent is directed to predicting aerodynamic and gasdynamic instabilities in turbofan engines. An instability precursor signal is generated in real time to predict engine surge or blade flutter in an air propulsion compression system for a turbofan engine utilizing a multistage axial compressor. An energy wave associated with aerodynamic or gasdynamic resonance in a compression system for a turbofan engine is detected and a signal indicative of the frequency of the resonance is generated. A static pressure transducer or strain gauge is installed near or attached to the fan blade to detect the energy of the system. The real-time signal is bandpass filtered within a predetermined range of frequencies associated with the instability of interest, eg, 250-310 Hz. The bandpass signal is then squared with respect to magnitude. The squared signal is then low pass filtered to form an energy instability precursor signal. The low-pass filter gives the average sum of squares of each frequency. The energy instability precursor signal is then used to predict aerodynamic and aerodynamic instabilities and prevent the aerodynamic and aerodynamic instabilities from occurring in a turbofan engine. One drawback of this technique is that it is only for the detection of impeller turning stalls in axial compressors and does not consider diffuser turning stalls.

  Mixed flow centrifugal compressors with vaneless radial diffusers can become diffuser swirl stalls during a portion of their intended operating range, or in some cases all of them. Typically, diffuser swirl stalls occur because the diffuser design cannot adapt all flows without a portion of the flow being separated in the diffuser passage. Diffuser swirl stall typically results in the production of low frequency sonic energy or pulsations in gas flow passages at a fundamental frequency that is less than the rotational frequency of the compressor impeller. This low frequency sound energy and its associated harmonics propagate through the compressor gas path to downstream pipes, heat exchangers and other vessels. Low frequency sound energy or acoustic disturbances can be high in magnitude and are undesirable. This is because the presence of acoustic disturbances can lead to early failure of the compressor, its controller, or other related components / systems.

  Therefore, what is needed is to detect and correct the rotational stall in the diffuser by sensing the change in acoustic energy in the gas flow around the diffuser of the centrifugal compressor, and then perform the action of changing the compression process, A system and method that avoids or corrects those conditions that generate a significant amount of swivel stall noise in the diffuser.

  The present invention can use either an analog circuit or a digital circuit (or a combination of the two circuits) to detect the presence of a rotating stall in the diffuser. The circuit uses a high-pass filter with a corner frequency of 10 Hz to process the signal from a pressure transducer located at or downstream from the diffuser to provide AC (or dynamic) variation from the pressure transducer. Can be analyzed. Next, a frequency above the break frequency of 300 Hz is attenuated using a low-pass filter. The operation of the low pass filter and the high pass filter can be considered similar to the operation of a band pass filter having a bandwidth of 10 Hz to 300 Hz. The 10-300 Hz range is important because the amplitude of the AC component in this range increases as the operation of the centrifugal compressor moves toward rotational stall.

  The output of the low pass filter or band pass filter is processed using an active full wave rectifier to obtain a positive only signal, which contains a composite AC component superimposed on the DC component. The composite signal produces a DC (or average) value that increases in magnitude as the stall frequency energy amplitude increases, and that DC value is required for subsequent processing. A low pass filter follows the active full wave rectifier. The low pass filter has a very low cut-off frequency of approximately 0.16 Hz to pass only the DC component of the waveform because the DC portion of the waveform provides an indication of the pressure transducer's stall fluctuation amplitude. The DC component or signal is then compared to a threshold value to determine the presence of turning stall. The threshold for determining the turning stall depends on the amount of gain applied to the signal from the pressure transducer and the amount of turning stall that can be tolerated by the diffuser before requesting correction.

  Alternatively, the present invention can utilize a DSP programmed to perform a fast Fourier transform (FFT) in real time on the digitized output of the pressure transducer to detect rotational stall. The use of FFT allows stall to be detected directly in the frequency domain rather than in the time domain as described above. The FFT is applied to the signal from the pressure transducer to obtain a series of frequencies and energy levels. Some of the frequencies from the FFT that are outside the range of interest (10-300 Hz) can be discarded. Next, energy levels between 10-300 Hz are summed to produce a summed energy level value. The energy level associated with the impeller rotational speed can be discarded for a more accurate value. The summed energy level value is then compared to a threshold value to determine the presence of a turning stall. Rather than adding spectral components, stall can be detected by looking for spectral peaks that exceed a predetermined threshold.

  One embodiment of the present invention is directed to a method of correcting for rotational stall in a radial diffuser of a centrifugal compressor. The method includes the step of measuring a value representing acoustic energy associated with rotational stall in a radial diffuser of a centrifugal compressor. The method further includes filtering the measured value using a bandpass filter to obtain a filtered value, and rectifying the filtered value using a full-wave rectifier to produce a rectified value. And filtering the rectified value with a low pass filter to obtain a stall energy component. Finally, the method includes the step of comparing the stall energy component with a predetermined value to determine a turning stall in the radial diffuser, wherein the turning stall is applied to the radial diffuser when the stall energy component is greater than the predetermined value. And the method further includes the step of sending a control signal to the centrifugal compressor in response to the determination of the rotational stall to adjust the mode of operation of the centrifugal compressor.

  Another embodiment of the present invention is directed to a method for detecting swirling stall in a centrifugal compressor. The method includes measuring a value representing acoustic energy associated with a rotational stall in a centrifugal compressor, and performing a fast Fourier transform on the measured value to obtain a plurality of frequencies and corresponding energy values. Including. The method also includes selecting a frequency and corresponding energy value associated with the turning stall from the plurality of frequencies and corresponding energy values, and adding the corresponding energy values of the selected frequency associated with the turning stall. Including the step of. Finally, the method includes detecting a turning stall in the centrifugal compressor by comparing the summed energy value with a predetermined threshold, wherein the summing stall is when the summed energy value is greater than the pre-determined threshold. Is present in the centrifugal compressor.

  Yet another embodiment of the present invention is directed to a system for correcting rotational stall in a radial diffuser of a centrifugal compressor. The system includes a sensor configured to measure a parameter representative of acoustic energy associated with rotational stall in a radial diffuser of a centrifugal compressor and generate a sensor signal corresponding to the measured parameter. The system also includes a high pass filter having a corner frequency of 10 Hz, a first low pass filter having a corner frequency of 300 Hz, and a full wave rectifier. The high pass filter is configured to receive the sensor signal and output a high pass filtered signal. The first low-pass filter is configured to receive the high-pass filtered signal from the high-pass filter and output the low-pass filtered signal. The full wave rectifier is configured to receive the low pass filtered signal and output a rectified signal. The system also includes a control circuit and a second low pass filter configured to receive the rectified signal and output a stall energy component signal. The control circuit is configured to determine a turning stall in the radial diffuser using the stall energy component signal and output a control signal in response to the determination of the turning stall to adjust the operation mode of the centrifugal compressor. .

  A further embodiment of the present invention is directed to a system for correcting rotational stall in a radial diffuser of a centrifugal compressor. The system includes a sensor configured to measure a parameter representative of acoustic energy associated with rotational stall in a radial diffuser of the centrifugal compressor and generate a sensor signal corresponding to the measured parameter. The analog / digital converter converts the sensor signal into a digital signal. The system also includes a digital signal processor that receives the digital signal from the analog to digital converter. The digital signal processor includes a high pass filter having a corner frequency of 10 Hz, a first low pass filter having a corner frequency of 300 Hz, a full wave rectifier, and a second low pass filter. The high pass filter is configured to receive a digital signal and output a high pass filtered signal. The first low pass filter is configured to receive a high pass filtered signal from the high pass filter and to output a low pass filtered signal. The full wave rectifier is configured to receive a low pass filtered signal and to output a rectified signal. The second low pass filter is configured to receive the rectified signal and output a stall energy component signal having only an average value of the rectified signal. A digital / analog converter is used to convert the stall energy component signal into an analog signal. Finally, the system is configured to use the analog signal to determine a turning stall in the radial diffuser and to output a control signal in response to the turning stall determination to adjust the operation mode of the centrifugal compressor. Control circuit.

  One advantage of the present invention is that it uses a simplified package of electronics and hardware to detect rotational stall in the diffuser portion of a centrifugal compressor.

Another advantage of the present invention is that the turning stall determination can be used to determine possible techniques for reducing or eliminating turning stall noise generated in the diffuser.
Other features and advantages of the present invention will become apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention.

  Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like elements.

  A general system to which the present invention can be applied is shown by way of example in FIG. As shown, the HVAC, cooling or liquid cooling system 100 includes a compressor 108, a condenser 112, a water cooler or evaporator 126, and a control panel 140. The control panel 140 receives input signals from the system 100 that indicate the performance of the system 100 and sends signals to components of the system 100 to control the operation of the system 100. A typical liquid cooling system 100 includes many other features not shown in FIG. These features are intentionally omitted to simplify the drawing for ease of explanation.

  The compressor 108 compresses the refrigerant vapor and supplies the vapor to the condenser 112 via a discharge line. The compressor 108 is preferably a centrifugal compressor. However, the present invention can be used with any type of compressor that can operate in a flow where a swirl stall condition is encountered or where swirl stall can occur. The refrigerant vapor supplied to the condenser 112 enters a heat exchange relationship with a fluid, such as air or water, and undergoes a phase change to a refrigerant liquid as a result of the heat exchange relationship with the fluid. The condensed liquid refrigerant from the condenser 112 flows to the evaporator 126. In the preferred embodiment, the refrigerant vapor of the condenser 112 enters a heat exchange relationship with water and flows through a heat exchanger coil 116 connected to the cooling tower 122. The refrigerant vapor in the condenser 112 undergoes a phase change to the refrigerant liquid as a result of the heat exchange relationship with the water in the heat exchanger coil 116.

  The evaporator 126 may preferably include a heat exchanger coil 128 having a supply line 128S and a return line 128R connected to the cooling load 130. The heat exchanger coil 128 can include a plurality of tube bundles in the evaporator 126. The secondary liquid is preferably water, but can be any other suitable secondary liquid, such as ethylene, calcium chloride brine, or sodium chloride brine, and evaporates via return line 128R. Proceed to evaporator 126 and exit evaporator 126 via supply line 128S. The liquid refrigerant in the evaporator 126 enters a heat exchange relationship with the secondary liquid in the heat exchanger coil 128 and cools the temperature of the secondary liquid in the heat exchanger coil 128. The refrigerant liquid in the evaporator 126 undergoes a phase change to refrigerant vapor as a result of the heat exchange relationship with the secondary liquid in the heat exchanger coil 128. The vapor refrigerant in the evaporator 126 exits the evaporator 126 and returns to the compressor 108 through the suction line to complete the circulation. Although the system 100 has been described with respect to a preferred embodiment with respect to the condenser 112 and evaporator 126, if an appropriate phase change of the refrigerant in the condenser 112 and evaporator 126 is obtained, the condenser 112 and evaporator It should be appreciated that any suitable form of 126 can be used with system 100.

  At the input or inlet to the compressor 108 from the evaporator 126 is one or more pre-rotating vanes or inlet guide vanes 120 that control the flow of refrigerant to the compressor 108. Using an actuator, the pre-rotation vane 120 is opened to increase the amount of refrigerant to the compressor 108 and thereby increase the cooling capacity of the system 100. Similarly, an actuator is used to close the pre-rotation vane 120 to reduce the amount of refrigerant to the compressor 108, thereby reducing the cooling capacity of the system 100.

  To drive the compressor 108, the system 100 includes a motor or drive mechanism 152 for the compressor 108. Although the term “motor” is used for the drive mechanism for the compressor 108, the term “motor” is not limited to a single motor, but relates to driving a motor 152 such as a variable speed drive and a motor starter. It should be understood that it is intended to encompass any component that can be used. In a preferred embodiment of the present invention, the motor or drive mechanism 152 is an electric motor and related components. However, other drive mechanisms such as steam or gas turbines or engines and related components can be used to drive the compressor 108.

  FIG. 2 shows a partial cross-sectional view of the compressor 108 of the preferred embodiment of the present invention. The compressor 108 includes an impeller 202 for compressing the refrigerant vapor. Thus, the compressed steam passes through the diffuser 119. The diffuser 119 is preferably a vaneless radial diffuser and has a diffuser space 204 formed between the diffuser plate 206 and the nozzle base plate 208 for the passage of refrigerant vapor. The nozzle base plate 208 is configured for use with the diffuser ring 210. A diffuser ring 210 is used to control the velocity of the refrigerant vapor through the diffuser passage 202. The diffuser ring 210 can be extended into the diffuser passage 202 to increase the speed of the refrigerant vapor flowing through the diffuser passage 202, and the diffuser ring 210 can be retracted from the diffuser passage 202 to cause the diffuser passage 202 to The speed of the flowing refrigerant vapor can be reduced. The adjustment mechanism 212 can be used to extend and retract the diffuser ring 210.

  Referring back to FIG. 1, the system 100 also includes a sensor 160 that senses the operating state of the system 100, which can be used to determine a turning stall condition in the diffuser 119. Sensor 160 can be located anywhere in the gas flow path downstream of impeller 202 of compressor 108. However, the sensor 160 is preferably located in the compressor discharge passage, or diffuser 119 (as schematically illustrated in FIG. 1). The sensor 160 is preferably a pressure transducer for measuring sound pressure or sound pressure phenomena, but other types of sensors may be used. For example, an accelerometer can be used to measure vibration associated with stall. The pressure transducer generates a signal representative of stall energy present in the discharge line. The signal from the sensor 160 is transferred to the control panel 140 via a line for subsequent processing to determine and correct the turning stall in the diffuser 119.

  The output of the sensor 160 used to measure the energy associated with the turning stall is preferably conditioned to distinguish between acoustic energy associated with the stall and energy due to other sources or vibration sources. In one embodiment of the invention, the conditioning can be done by simply measuring the amount of energy in a frequency range that includes the stall fundamental frequency and its major harmonics. In other conditioning schemes, in order to enhance the ability to detect the presence of only turning stall energy, some frequencies not associated with stall in the stall related area could be sensed and removed from the analysis. The conditioned output signal from sensor 160 can be used in conjunction with the process described below to perform a corrective action to avoid a significant amount of turning stall noise generated by compressor 108.

  The contents of the intensity and frequency of sound energy associated with turning stall were studied extensively. As the compressor operation moves into the swirl stall region, the AC component of the acoustic energy increases within a predetermined frequency band of approximately 10-300 Hz. It was also observed that the arrival of a significant amount of turning stall was rather sudden. Therefore, a frequency analysis of the signal representing the acoustic energy present in the gas flow shows that a sudden increase in energy intensity or magnitude associated with stall in the 10-300 Hz frequency band may cause the compressor to enter into a stall stall condition. Indicates that it represents moving.

  FIG. 3 shows one process for detecting and correcting a rotating stall in the diffuser 119 of the compressor 108. This process uses analog components (parts schematically shown in FIG. 4), digital components (parts shown schematically in FIG. 5), or a combination of analog and digital components (not shown). Can be executed on the control panel 140. The process begins at step 302 where the control panel 140 receives a signal from the sensor 160. As described above, the signal received from sensor 160 corresponds to an amount of energy that indicates the beginning of a turn stall. Direct measurement of the sound pressure phenomenon using the pressure sensor 160 in the preferred embodiment provides a more reliable indication of the presence of a turning stall and avoids other acoustic signals associated with non-stall. For example, if the vibration of the compressor 108 is used to detect the beginning of a swing stall, any vibration due to an imbalance in the compressor motor 152 or gear or impeller 202 that may be in the same frequency range as the swing stall noise is Signals of such magnitude can be provided that can hinder their ability to detect only components related to turning stall noise.

  In step 304, the signal from sensor 160 is passed through a high pass filter. In determining the presence of turning stall, the AC variation from sensor 160 represents the signal of interest, and the DC portion of the signal is not required for detection of turning stall. Therefore, a high pass filter is used to remove the DC portion of the signal. The high pass filter preferably has a corner frequency of about 10 Hz. The corner frequency can be set to an appropriate value that removes the DC portion of the signal while leaving a sufficient AC portion of the signal for analysis depending on the desired detection accuracy. In one embodiment of the present invention, the high pass filter may include a single pole RC high pass filter that provides an input signal attenuation of 0.707 at 10 Hz, which is DC (0 Hz) below this frequency. ) To zero. In other embodiments of the present invention, higher order high pass filters can be used to filter the signal from sensor 160.

  After passing through the high pass filter and gain amplifier (if necessary), the signal is passed through a low pass filter in step 306. The low-pass filter is used to attenuate frequencies above the corner frequency or cut-off frequency. Note that the break frequency defines the upper frequency level associated with the turning stall condition. In a preferred embodiment of the present invention, the upper frequency or corner frequency associated with the turning stall energy is about 300 Hz. In one embodiment of the present invention, a frequency component above a stall frequency range (approximately 300 Hz) that is not associated with a turn stall, which may result in a false indication of a turn stall using a 6th order Butterworth low pass filter. Remove. In other embodiments of the present invention, higher order low pass filters can be used to remove higher frequencies, preferably higher orders.

  In another embodiment of the present invention, steps 304 and 306 can be combined into a single step. In this embodiment, instead of using both a high pass filter (step 304) and a low pass filter (step 306), both a DC component and a higher frequency from the sensor signal are used using a band pass filter. Can be removed. The bandpass filter preferably has a frequency range of about 10-300 Hz, which is the equivalent frequency range after the high and low pass filters of steps 304 and 306.

  After passing through the low pass filter in step 306, the signal is passed to an active full wave rectifier in step 308. The active full-wave rectifier is used to convert or “flip” the negative portion of the AC signal to an equal positive value while not affecting the positive portion of the AC signal. The full wave rectified signal has only a positive component and includes a composite of AC components superimposed on the DC component. This composite signal results in an average (or DC) value that increases in magnitude as the amplitude of energy at the stall frequency increases.

  In step 310, the signal from the active full wave rectifier is passed through a low pass filter having a low cutoff frequency to pass only the DC component. As described above, the DC component portion of the full-wave rectified waveform provides an indication of the stall fluctuation amplitude of the sensor 160, so that only the DC component of the signal is necessary for detection of turning stall. In one embodiment of the present invention, the low pass filter may have a cutoff frequency of 0.16 Hz. However, this frequency is not critical and other cutoff frequencies, eg 0.1 Hz, can be used to pass only the DC component.

  FIG. 4 schematically illustrates an analog circuit that performs all steps 304-310. High pass filter 402 receives the signal from sensor 160, which filters the signal as described with respect to step 304. If necessary, the gain amplifier 404 can be used to increase or enhance the output from the high pass filter 402. The gain amplifier 404 can be used to increase the signal from the high pass filter 402 to an appropriate value for comparison with a threshold value representing a turn stall condition. Low pass filter 406 receives the signal from gain amplifier 404 or high pass filter 402 and filters the signal as described with respect to step 306. An active full wave rectifier 408 is used to rectify the signal from the low pass filter 406 as described above with respect to step 308. An active full wave rectifier 408 is preferred to eliminate the DC offset that can be generated by using a full wave bridge rectifier. Finally, the full wave rectified signal from active full wave rectifier 408 is filtered using low pass filter 410, which filters the signal as described above with respect to step 310, The signal is then sent to the control circuit. Note that the control circuit may include a microprocessor and / or a comparator for subsequent processing of the signal from the low pass filter 410.

  FIG. 5 schematically illustrates a digital circuit that performs all steps 304-310. If necessary, the gain amplifier 502 can be used to increase or enhance the signal from the sensor 160 to an appropriate value for comparison with a threshold representing a turn stall condition. The signal from gain amplifier 502 or sensor 160 is then passed to A / D converter 504 to convert the analog signal to a digital signal. The digital signal from A / D converter 504 is then preferably provided to a digital signal processor (DSP) circuit 506 for performing all steps 304-310. In the DSP circuit 506, the high pass filter 508 receives the signal from the A / D converter 504, and the high pass filter 508 filters the signal as described with respect to step 304. Low pass filter 510 receives the signal from high pass filter 508 and filters the signal as described with respect to step 306. A full wave rectifier 512 is used to filter the signal from the low pass filter 510 as described with respect to step 308. The full wave rectified signal from full wave rectifier 512 is filtered using low pass filter 514, which filters the signal as described with respect to step 310. Finally, the signal from the low pass filter 514 of the DSP circuit 506 is passed to a D / A converter 516, which generates an analog signal and passes the analog signal to the control circuit. send. Note that the control circuitry may include a microprocessor and / or a comparator for subsequent processing of the analog signal.

  Referring back to FIG. 3, the low pass filtered signal having only the DC component from step 310 is compared to a threshold at step 312 to determine the presence of turning stall. As described above, the magnitude of the DC component increases as the compressor 108 moves to the turning stall condition. Thus, the presence of turning stall can be detected by determining when the DC component or voltage exceeds a threshold. The threshold value can be set to a value that is a normal operating value for the DC component, that is, a multiple of the value of the DC component when there is no turning stall. In a preferred embodiment of the present invention, the threshold can be 2 to 6 times the normal operating value. For example, if the normal operating value for the DC component is 0.2-0.4 VDC, the threshold for detecting the turning stall can be between 0.8 VDC and 1.2 VDC. The value for normal operation and the value for the threshold depend on the amount of gain applied to the signal. In other words, when the gain applied to the signal is larger, the normal operating value is larger and the threshold is larger. If no turning stall is detected at step 312, the process returns to step 302 and a new signal from sensor 160 is obtained for processing.

  If a turning stall is detected in step 312, a correction operation is performed in step 314 to correct the turning stall condition. The corrective action can reduce the width of the diffuser space 204 of the radial diffuser 119, reduce the length of the radial diffuser 119, or increase the flow to the compressor 108 at the compressor inlet or downstream of the impeller 202. However, it is not limited to this. In a preferred embodiment of the present invention, upon detection of a turning stall, the control panel 140 sends a signal to the diffuser 119, in particular to the adjustment mechanism 212 of the diffuser 119, to adjust the position of the diffuser ring 210, Correct the turning stall condition. The diffuser ring 210 is inserted into the diffuser space 204 to reduce the width of the diffuser space 204 in order to correct the turning stall condition.

  In another embodiment of the present invention, the presence of a turning stall can be detected using Fast Fourier Transform (FFT). FIG. 6 illustrates one process that uses FFT to detect and correct for rotational stall in the diffuser 119 of the compressor 108. The process begins at step 602 with control panel 140 receiving a signal from sensor 160, and at step 604, preferably using an A / D converter, converts the signal from sensor 160 to a digital signal. . Next, in step 606, an FFT is applied to the signal from step 604 to generate a plurality of frequencies and energy values. The FFT is preferably programmed into a DSP chip on the control panel 140 and can be executed in real time. The FFT DSP chip is preferably configured to perform any necessary operations or calculations such as multiplication and accumulation to complete the FFT. By applying an FFT to the digitized input signal from sensor 160, it is possible to detect turning stalls directly in the frequency domain rather than in the time domain as described above with respect to FIG.

  Since only a specific range of fundamental frequencies, i.e., about 10-300 Hz as described in more detail above, is of interest in detecting swirling stalls, only those specific frequencies of interest in the step 608 are frequency domain Must be analyzed, i.e. frequencies that are not associated with turning stalls can be discarded. Furthermore, the fundamental frequency of the particular range of interest is always less than or equal to the rotational frequency of the compressor impeller 202, so that the analysis of the swirling stall can be made more appropriate by considering the compressor speed. It can be limited to a range. This limitation of the frequency range of interest is advantageous in variable speed drive (VSD) applications. This is because as the speed of the impeller 202 is reduced, the frequency range of interest becomes narrower, thereby helping to eliminate irrelevant frequencies that would lead to false detections. If the compressor tries to operate at a variable speed or a fixed speed, the frequency component and its harmonics associated with the impeller operating speed are removed (set to zero), while the frequency component of the FFT associated with the rotating stall and its Harmonics are preserved. Other non-stall frequencies (60 Hz and harmonics) below the rotational frequency of the compressor impeller 202, such as an electronic interface that can be coupled through a transducer, can also be removed.

  After elimination of irrelevant frequencies in step 608, the remaining components or frequencies from the FFT are added together in step 610 to determine if the resulting value is within the turning stall range. Similar to the detection of turning stall in step 312, the detection of turning stall in step 610 is based on the summed or resulting value being greater than a threshold value that defines the stalled region. The threshold is a value equal to a multiple of the normal operating value relative to the summed or resulting value from the FFT component, i.e. the summed or resulting value from the FFT component when there is no turning stall. Can be set to a value. In a preferred embodiment of the invention, the threshold can be 2 to 6 times the normal operating value. The values for normal operation and threshold depend on the strength of the signal being analyzed and the amount of amplification applied to the signal to enhance the signal to noise ratio. In another embodiment of the present invention, turning stall can be detected by determining whether the peak of the remaining frequency spectrum exceeds a predetermined threshold. If, in step 610, no turning stall is detected, the process returns to step 602 and a new signal from sensor 160 is obtained for processing.

  If a turning stall is detected in step 610, a correction operation is performed in step 612 to correct the turning stall condition. The corrective action can reduce the width of the diffuser space 204 of the radial diffuser 119, reduce the length of the radial diffuser 119, or increase the flow to the compressor at the compressor inlet or downstream of the impeller 202. However, it is not limited to these. In a preferred embodiment of the present invention, upon detecting a turning stall, the control panel 140 sends a signal to the adjusting mechanism 212 of the diffuser 119 to adjust the position of the diffuser ring 210 to correct the turning stall condition. . The diffuser ring 210 is inserted into the diffuser space 204 in order to correct the turning stall condition, and the width of the diffuser space 204 is narrowed.

  Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that various modifications can be made and components of the invention can be replaced by equivalents without departing from the scope of the invention. Will be understood. Moreover, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Accordingly, the invention is not limited to the specific embodiments disclosed as the best mode contemplated for carrying out the invention, but the invention includes all aspects that fall within the scope of the appended claims. Is intended.

FIG. 1 schematically illustrates the cooling system of the present invention. FIG. 2 shows a partial cross-sectional view of the centrifugal compressor and diffuser of the present invention. FIG. 3 shows a flow chart for detecting and correcting a turning stall condition in an embodiment of the present invention. FIG. 4 schematically illustrates one embodiment of an analog circuit for use with the present invention. FIG. 5 schematically illustrates one embodiment of a digital circuit for use with the present invention. FIG. 6 shows a flow chart for detecting and correcting a turning stall condition in another embodiment of the present invention.

Claims (41)

A method of correcting a rotating stall in a radial diffuser of a centrifugal compressor,
Measuring a value representative of acoustic energy associated with rotational stall in a radial diffuser of a centrifugal compressor;
Filtering the measured value with a bandpass filter to obtain a filtered value;
Rectifying the filtered value with a full wave rectifier to obtain a rectified value;
Filtering the rectified value with a low pass filter to obtain a stall energy component;
Comparing the stall energy component with a predetermined value and determining a turning stall in the radial diffuser that is present in the radial diffuser when the stall energy component is greater than the predetermined value;
In response to determining the rotational stall, sending a control signal to the centrifugal compressor to adjust the mode of operation of the centrifugal compressor;
A method comprising:   The method of claim 1, wherein the step of measuring a value representative of acoustic energy associated with rotational stall comprises the step of measuring an acoustic pressure at a radial diffuser of the centrifugal compressor with a pressure transducer.   The method of claim 2, wherein the pressure transducer is disposed in a compressor discharge passage. The step of filtering the measured value with a band pass filter;
Filtering the measured value with a high-pass filter having a corner frequency of 10 Hz to obtain an intermediate value;
Filtering the intermediate value with a low-pass filter having a corner frequency of 300 Hz;
The method of claim 1 comprising:   The method of claim 4, wherein the high pass filter is a single pole RC high pass filter and the low pass filter is a sixth order Butterworth low pass filter.   The method of claim 4, further comprising amplifying the intermediate value with a gain amplifier.   The method of claim 1, wherein the full wave rectifier is an active full wave rectifier.   Filtering the rectified value with a low-pass filter to obtain a stall energy component includes filtering the rectified value with a low-pass filter having a cutoff frequency of 0.16 Hz; The method of claim 1.   The method of claim 1, wherein the predetermined value is a multiple of a stall energy component calculated during normal operation of the centrifugal compressor without a rotating stall.   The method according to claim 9, wherein the predetermined value is 2 to 6 times the stall energy component calculated during normal operation of the centrifugal compressor without turning stall.   The method of claim 1, wherein the step of sending a control signal to the centrifugal compressor comprises sending a control signal to the radial diffuser.   The method of claim 11, further comprising adjusting a diffuser ring and reducing the width of the diffuser space in response to the control signal sent to the radial diffuser.   The method of claim 1, further comprising amplifying the measured value with a gain amplifier.   The method of claim 1, further comprising conditioning the measured value to remove acoustic energy not associated with turning stall. Measuring a value representative of acoustic energy associated with rotational stall in a centrifugal compressor;
Performing a fast Fourier transform on the measured values to obtain a plurality of frequencies and corresponding energy values;
Selecting a frequency associated with a turning stall and a corresponding energy value from the plurality of frequencies and energy values;
Adding the corresponding energy values of selected frequencies associated with the turning stall;
Detecting the rotational stall of the centrifugal compressor by comparing the summed energy value with a predetermined threshold, and
Rotating stall is present in the centrifugal compressor when the added energy value is greater than the predetermined threshold.
A method for correcting a rotating stall in a centrifugal compressor.   The method of claim 15, wherein the step of measuring a value representative of acoustic energy associated with rotational stall comprises measuring the acoustic pressure at a radial diffuser of the centrifugal compressor with a pressure transducer.   The method of claim 16, wherein the pressure transducer is disposed in a compressor discharge passage.   The method of claim 15, wherein the step of selecting a frequency and a corresponding energy value associated with a turning stall includes selecting a frequency and a corresponding energy value in a frequency range of about 10 Hz to about 300 Hz.   The method of claim 18, further comprising removing a frequency and a corresponding energy value that are not associated with a turning stall from a frequency range of about 10 Hz to about 300 Hz.   The method of claim 15, wherein the predetermined threshold is a multiple of the added energy value calculated during normal operation of the centrifugal compressor without a rotating stall.   21. The method according to claim 20, wherein the predetermined threshold is 2 to 6 times the added energy value calculated during normal operation of the centrifugal compressor without turning stall. Generating a control signal for the radial diffuser of the centrifugal compressor in response to detection of a rotating stall;
The method of claim 15, further comprising: sending the generated control signal to the radial diffuser to change the shape of the radial diffuser.   23. The method of claim 22, further comprising adjusting a diffuser ring to reduce the width of the diffuser space in the radial diffuser in response to the generated control signal also being sent to the radial diffuser. .   The method of claim 15, further comprising amplifying the measured value with a gain amplifier.   16. The method of claim 15, further comprising conditioning the measured value to remove acoustic energy not associated with turning stall. A system for correcting rotational stall in a radial diffuser of a centrifugal compressor,
A sensor configured to measure a parameter representative of acoustic energy associated with rotational stall in a radial diffuser of a centrifugal compressor and to generate a sensor signal corresponding to the measured parameter;
A high pass filter having a corner frequency of 10 Hz, configured to receive the sensor signal and to output a high pass filtered signal;
A first low pass filter having a corner frequency of 300 Hz, configured to receive the high pass filtered signal from the high pass filter and to output a low pass filtered signal;
A full wave rectifier configured to receive the low pass filtered signal and to output a rectified signal;
A second low pass filter configured to receive the rectified signal and output a stall energy component signal;
A control circuit configured to determine a turning stall in the radial diffuser using the stall energy component signal, and to adjust a mode of operation of the centrifugal compressor by outputting a control signal in response to the turning stall determination. A system comprising:   27. The system of claim 26, wherein the sensor comprises a pressure transducer for measuring acoustic pressure in a radial diffuser of the centrifugal compressor.   28. The system of claim 27, wherein the pressure transducer is disposed in a discharge passage of the centrifugal compressor during installation of the pressure transducer.   27. The system of claim 26, wherein the high pass filter is a single pole RC high pass filter.   27. The system of claim 26, wherein the low pass filter is a sixth order Butterworth low pass filter.   27. The system of claim 26, further comprising a gain amplifier configured to receive the high pass filtered signal and output the amplified signal to the first low pass filter.   27. The system of claim 26, wherein the full wave rectifier is an active full wave rectifier.   27. The system of claim 26, wherein the second low pass filter has a corner frequency of 0.16 Hz. The control circuit includes a comparator for comparing the stall energy component signal with a predetermined value;
The control circuit outputs the control signal in response to the stall energy component signal being greater than a predetermined value;
The predetermined value is a multiple of a stall energy component calculated during normal operation of the centrifugal compressor without turning stall.
27. The system of claim 26.   35. The system of claim 34, wherein the predetermined value is between two and six times the value of the stall energy component calculated during normal operation of the centrifugal compressor without turning stall. A sensor configured to measure a parameter representing acoustic energy associated with rotational stall in a radial diffuser of the centrifugal compressor and to generate a sensor signal corresponding to the measured parameter;
An analog / digital converter for converting the sensor signal into a digital signal;
A digital signal processor for receiving the digital signal from the analog / digital converter;
The digital signal processor comprises:
A high pass filter having a corner frequency of 10 Hz, adapted to receive the digital signal and to output a high pass filtered signal;
A first low pass filter having a corner frequency of 300 Hz, configured to receive the high pass filtered signal from the high pass filter and to output a low pass filtered signal;
A full wave rectifier configured to receive the low pass filtered signal and to output a rectified signal;
A second low pass filter configured to receive the rectified signal and to output a stall energy component signal;
A digital / analog converter for converting the stall energy component signal into an analog signal;
A control circuit configured to determine a rotational stall in the radial diffuser using the analog signal, and to output a control signal in response to the determination of the rotational stall to adjust an operation mode of the centrifugal compressor;
The system which correct | amends the rotation stall in the radial diffuser of a centrifugal compressor provided with.   40. The system of claim 36, wherein the sensor comprises a pressure transducer for measuring acoustic pressure in a radial diffuser of the centrifugal compressor.   38. The system of claim 37, wherein the pressure transducer is disposed in a discharge passage of the centrifugal compressor during installation of the pressure transducer.   38. The system of claim 36, further comprising a gain amplifier configured to receive the measured signal and output an amplified signal to the analog / digital converter. The control circuit comprises a comparator for comparing the stall energy component signal with a predetermined value;
The control circuit outputs the control signal in response to the stall energy component signal being greater than a predetermined value;
The predetermined value is a multiple of a stall energy component calculated during normal operation of the centrifugal compressor without turning stall.
37. The system of claim 36.   41. The system of claim 40, wherein the predetermined value is between two and six times the value of the stall energy component calculated during normal operation of the centrifugal compressor without turning stall.

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